This invention relates generally to feeders for pulverulent dry materials such as fine powders, as well as for flakes, granules, chips, pellets and pebbles that are difficult to feed from hoppers at continuous, controllable volumetric rates. The spectrum of such materials includes, for example, ceramics, cosmetics, plastics, foods and pharmaceuticals.
Problems frequently encountered in producing uniform, controllable volumetric feed rates of such particulate materials include erratic metering of the flow, exposure of the plant environment to the material, flooding of the material, surging or pulsating discharge from the feeder, erratic feeding of denser followed by lighter material, and compaction or clogging of the material in the hopper. It is desirable to promote and maintain, without the use of excessive manual labor, a constant, uniform flow of the material from the hopper, without producing material degradation or compaction.
To overcome these problems, various systems have been employed. These have included a variety of means such as massaging paddles or plates to flex the hopper walls, and other means to create pulsating, vibrating, undulating, flexing, agitating or otherwise activated movement of the hopper walls or of panels within or adjacent the hopper walls. Still other devices have employed multiple auger and agitator means such as a large auger and a small or metering auger. Various other forms of internal stirring devices have also been employed.
The volumetric dry material feeders in prior use have been developed for applications such as proportioning materials in processing operations, continuous mixes and bag loading applications, for example. A common problem in these applications arises when such materials are delivered from a hopper to a feeder, which may be a screw or auger feeder, a belt feeder or the like. The material within the hopper tends to discharge erratically because of the formation of bridging or stable arch formations, rat holes, tunnels or funnels which may form and intermittently collapse. The material is also subject to compaction and clogging which may interrupt or completely stop the flow. As a result, it is difficult to obtain accurate volumetric metering of the material and a precisely controllable feed rate.
A principal object of this invention is to provide an improved dry material feeder that permits the attainment of a constant and accurately adjustable volumetric feed rate. A related object is to provide means for readily adjusting the operation of the feeder to maintain proper flow conditions by observation of the material and adjustment as it is flowing, and thereby to maintain the desired flow rate.
Another object is to provide a feeder adapted for feeding a wide range of materials including those that are extremely difficult to feed at a constant rate due to the persistence of the above-mentioned flow interrupting phenomena.
Still further objects are to provide a feeder having a hopper construction of reduced cost with a minimum exposure of fasteners or other devices to the material within the hopper, and to provide for the replacement in less expensive form of parts that come in contact with the material.
Another object is to provide a feeder that presents minimum hazards to worker safety in operation, with minimal danger of discharge of dry material powders or particulates into the surrounding environment.
With the above and other objects in view, as hereinafter appearing, the features of this invention include a movable wall hopper forming mutually opposing sloping wall portions, each having a thrust plate supported adjacent thereto and movable alternately between positions mutually displaced relative to the wall portion. The thrust plates are located to displace the material in opposing directions by reciprocating movement, thereby displacing the material within the hopper. The thrust plates are each provided with driving means adapted to reciprocate the plates at different cycle frequencies and independently of the discharge auger speed, whereby the material in the hopper is displaced relative to the walls by a continually varying combination of the opposing thrust plate movements.
The hopper comprises lower and upper components that are adapted to nest together with a flexible diaphragm sheet clamped between them and overlying the mutually opposing sloping wall portions to form flexible wall panels The lower component comprises the opposing, sloping wall portions, and the upper component comprises the end panels of the hopper when in the nested position.
The flexible diaphragm is displaced by the thrust plates which are sandwiched between the diaphragm and the lower hopper wall portions. Means for actuating the thrust plates are mounted externally of the hopper in positions where their operation may be readily adjusted. Means for adjustment comprise timers for independently varying the cycle frequencies of alternate movements of the thrust plates, means for varying the rate at which the thrust plates displace the material, and means for varying the amplitudes of such movements while observing the effect upon the continuing flow of material from the hopper.
Other features of the invention will become evident from the following description with reference to the appended drawings.